Clear composition changes when a color mode is not supported

Otherwise this may cause a test to spuriously fail during teardown.

Bug: 184726169
Test: VtsHalGraphicsComposerV2_2TargetTest
Change-Id: I569680a0fe6c866199ba0711e8cc263b9b3efd58
diff --git a/graphics/composer/2.2/vts/functional/VtsHalGraphicsComposerV2_2ReadbackTest.cpp b/graphics/composer/2.2/vts/functional/VtsHalGraphicsComposerV2_2ReadbackTest.cpp
index 7a1568b..7a053f1 100644
--- a/graphics/composer/2.2/vts/functional/VtsHalGraphicsComposerV2_2ReadbackTest.cpp
+++ b/graphics/composer/2.2/vts/functional/VtsHalGraphicsComposerV2_2ReadbackTest.cpp
@@ -458,6 +458,7 @@
                           << " pixel format: PixelFormat::RGBA_8888 dataspace: "
                           << ReadbackHelper::getDataspaceString(clientDataspace)
                           << " unsupported for display" << std::endl;
+                mReader->mCompositionChanges.clear();
                 continue;
             }